Add support for setupFiles and snapshotSerializers

[fisker]

Prettier added these when using this module.
https://github.com/prettier/prettier/tree/next/tests/config/jest-light-runner

[fisker]

I'm going to test this on Prettier first. Done, works for us. prettier/prettier#12592

[fisker]

@SimenB, should setupFiles work like this?

We exposed setup function before, https://github.com/prettier/prettier/blob/3cbee742a792413211eea1e4fe2d0dad26ff37ea/tests/config/jest-light-runner/src/worker-runner.js#L30-L36

[nicolo-ribaudo]

Looking at the Jest source code (https://github.com/facebook/jest/blob/main/packages/jest-repl/src/cli/runtime-cli.ts#L112-L123=), we should do something like this:

const { default: setup } = await import(pathToFileURL(setupFile));
if (typeof setup === "function") await setup();

(technically Jest only calls setup() if it comes from a CJS file, but it's easier to always call it than to check the file type).

In Prettier's setup file, you could either:

• rewrite it to CJS, use dynamic imports in the setup function instead of top-level import declarations, and do module.exports = setup (this also works with Jest's default runner);
• export a function named then rather than setup, because await import(...) will automatically call then and await it since { then: function } is a promise-like object (this might also work with Jest's default runner);
• Use export default setup (and not export default setup()), so that it will be awaited because it's a function (this will only work with this runner, since Jest only calls the function for CJS files).

[SimenB]

yeah. we would like to call it for ESM as well, but there's no (supported) way of getting the exported result with vm APIs. So our plan there is to tell people to use TLA for ESM and exporting a function from CJS.

[nicolo-ribaudo]

Thanks! 😄

Could you also add them in the README to the "supported features" section?

[nicolo-ribaudo]

This should be enough, since the serializer is always stored on module.exports and thus becomes the default export:

const { default: serializer } = await import(pathToFileURL(snapshotSerializer));

Also, probably we should add them in reverse order: https://github.com/facebook/jest/blob/a20bd2c31e126fc998c2407cfc6c1ecf39ead709/packages/jest-circus/src/legacy-code-todo-rewrite/jestAdapterInit.ts#L149-L152

[fisker]

All review points addressed.

[nicolo-ribaudo]

Thanks! I'll add a CI job that tests this runner both with Babel's and Prettier's test suites, then I'll release a new version.

[fisker]

Thank you!

[fisker]

FYI: yarn test:format on next branch is what are we using.

[fisker]

I'm going to work on setting up Prettier's test.